Vitalism: How Chemistry Captured Life

Before the first chapter of any biochemistry course, there is a belief that had to die. For most of the history of science, the molecules of living things were thought to require living things to make them. Sugar, fat, urea, the acids of blood and muscle — all of it was supposed to carry a spark, a vital force, that ordinary matter did not have and chemistry could not supply. This was the organizing principle of chemistry itself — the line Berzelius built his entire system on — and the whole field of biochemistry is what happened when it fell.

The wall

By the early nineteenth century the most respected chemist in Europe was Jöns Jacob Berzelius, who gave the science its written alphabet — the letters H, O, and C, so a reaction could be written down rather than narrated. He also drew the era’s sharpest line. On one side was inorganic matter, the chemistry of rocks and salts and gases, which obeyed ordinary law. On the other was organic matter, the chemistry of living bodies, which did not. The wall between them rested on a single conviction: that the molecules of life required life to make them. It was the boundary Berzelius’s entire system stood on.

The student who would walk across it had trained in Berzelius’s own kitchen laboratory in Stockholm, and had once been told, after rushing an analysis, that the work was “quickly and badly done.” His name was Friedrich Wöhler.

Wöhler’s flask, 1828

In February 1828, Wöhler sat down to warm an inorganic salt called ammonium cyanate, and what crystallized in his flask was urea — the very molecule the body makes to dispose of nitrogen. There was no kidney in the room and no vital spark anywhere in the apparatus. He wrote to Berzelius with a confession he could not keep to himself: “I can no longer, as it were, hold back my chemical urine; and I have to let out that I can make urea without needing a kidney.”

Look closely at what had happened, because it is subtler than “he made life from non-life.” Urea and ammonium cyanate have the same molecular formula — CH₄N₂O, one carbon, four hydrogens, two nitrogens, one oxygen. They are the same atoms, connected differently. Heat simply rearranged the connections, and the rearrangement alone turned a lifeless salt into a signature of metabolism. The lesson Wöhler took was the one this whole course depends on: structure, not just composition, is what a molecule is.

Wöhler’s flask did not kill vitalism that afternoon, whatever the textbooks imply. His critics had an honest objection: ammonium cyanate could itself be traced back to organic sources, so perhaps he had only turned organic matter into organic matter. The vital force pulled back, but it had somewhere to stand. Wöhler, for his part, never claimed to have conquered anything. He called the field he had opened “a primeval forest, a monstrous and boundless thicket,” and claimed only to have entered it.

The seventy-year retreat

What followed was a fighting retreat spanning seventy years, each synthesis driving the vital force into a smaller corner.

In 1845 Hermann Kolbe, trained under Wöhler, built acetic acid by a route that left the loophole no room. He started from carbon disulfide — made from charcoal and molten sulfur, with nothing alive anywhere in the chain — and finished the reduction not with a cell or a seed but with an ordinary battery. Kolbe’s own aim was to prove a theory of how molecules are assembled, but the effect outran his intent: there was now no organic source to point to. (That two-carbon acetyl group he assembled from lifeless carbon turns out to be the busiest fragment in all of metabolism, carried as acetyl-CoA into the citric acid cycle in every cell you have.) A decade later Marcellin Berthelot went further still, building fats — a whole class of the body’s molecules — from glycerol and fatty acids, each bond forming by the same equilibrium chemistry as any mineral salt.

Molecule by molecule, the ground was disappearing. But one redoubt remained, and it was defended by the most formidable scientist of the age.

The last redoubt: fermentation

Louis Pasteur had proved that fermentation depended on living yeast: grape juice sealed from the air stayed inert, while juice open to airborne yeast foamed into alcohol. It was a true and important result. But from it Pasteur drew a line stronger than his data required — that fermentation was inseparable from the intact living cell. Pasteur invoked no vital force; his was an empirical conviction, and it carried the authority of the man who had just proven fermentation was alive. The “needs life” intuition had retreated from individual molecules to whole processes, and there it dug in for forty years.

The crack began with a word. In 1877 Wilhelm Kühne, who believed that vision and digestion and fermentation were all chemistry waiting to be lifted out of the cell, proposed a name for the soluble agent inside yeast: enzyme, from the Greek for “in leaven.” It named not the cell and not the tissue but the chemical worker within. The name implied a claim — that the worker could be separated from its workshop — and in 1897 Eduard Büchner separated it.

Büchner ground brewer’s yeast with sand, pressed out a clear golden juice with no intact cells in it, and added sugar to preserve it. The sugar began to ferment on its own, carbon dioxide rising through a flask of dead yeast, two years after the death of the man who had ruled it impossible. When the vitalists insisted that scraps of living protoplasm must have survived, Büchner answered with two controls: boiled juice did not ferment, so the agent was a destructible chemical; filtered juice still did, so no cells were needed. “The active agent in the expressed yeast juice appears to be a chemical substance, an enzyme,” he wrote. He named it zymase and took the 1907 Nobel Prize — often called the first ever given for a fundamentally biochemical discovery. The vital force was out of places to hide.

Why this is Chapter Zero

Seventy years of successive syntheses — Wöhler’s urea in 1828, Kolbe’s acetic acid, Berthelot’s fats, and finally Büchner’s cell-free fermentation in 1897 — made the vital force unnecessary, one molecule and one process at a time, until almost no ground was left for it to stand on. What replaced it is the single premise the rest of this book assumes without restating: a living cell obeys the same chemistry as everything else — weighable and accountable, with no separate law of its own.

Everything downstream is the working-out of that premise. The catalysts Kühne named and Büchner freed are ordinary proteins — a fact sealed in 1926 when James Sumner crystallized urease, the enzyme that takes urea back apart, and held a catalyst of life in his hand as a pile of crystals. The acetyl group Kolbe built from charcoal is the hub of metabolism. And urea itself, the molecule Wöhler conjured from a salt, is built in your liver right now by a ring of five enzymes called the urea cycle — the subject of one of the last chapters in this course. The thread that runs from his flask to that cycle is the whole discipline: life is chemistry, and chemistry can be measured, mapped, and understood.